The present invention is an improved processing apparatus for efficiently transferring heat from air to coffee beans to secure a uniform roasting thereof.
Accepted commercial coffee bean roasting methods have not undergone any significant recent improvements in efficiency or simplification. The principles employed in widely utilized coffee roasters are virtually the same as used over 50 years ago. One exception is that about 40 years ago a continuous rotary cylinder roasting machine was developed by the Jabez Burns & Sons, Inc. Company in the United States. The commonly utilized prior art roasters employed rotating steel cylindrical roast chambers which held the coffee bean charge occupying only about 15 percent of roast chamber volume, and which cylinder was rotated about a horizontal axis at rates of typically 60 to 90 revolutions per minute. Hot recirculatory gases are passed about and through the cylinder, but not necessarily through the beans therein, at temperatures from 650.degree. to 700.degree.F., or even higher. Coffee roasting times varied from 10 to 30 minutes, and uniform roasting of each bean was not routinely achieved.
Smoke, smog, organic fumes and aerosols of fine oil were abundantly liberated during roasting operations in such prior art coffee roasters. With the enactment and enforcement of air quality control standards by federal, state and municipal authorities, coffee roasting firms have become obligated to make large capital expenditures for air pollution control devices such as "after burners," the operation of which has doubled fuel consumption and operating costs.
The movement of hot gases through the roasting beans has not been positively controlled. Some beans were always scorched (tipped) or burned due to remaining in contact with the very hot metal cylinder walls more than a few seconds. The high temperature of the gases used permitted shortened roasting times, for example, 5 minutes, with the concomitant drawback that the beans were less uniformly roasted, many beans were scorched and excessive volatiles, vegetable oils, char and degraded organics were liberated from the beans which in turn degraded coffee flavor as well as generated abundant air pollutants.
Coffee volatiles are rich in aromatic aldehydes and ketones, chemical constituents which are very unstable at the temperatures typically found within these prior art roasting cylinders. In seconds, oxidized and polymerized byproducts were formed from liberated aldehydes, and these chemical byproducts became smokey, and by contact contaminated the clean beans being roasted, thereby adversely affecting the produced flavor quality. And, in combination with loosened chaff, these organic byproducts coated the cylinder walls and other apparatus with which they came into contact. Frequent cleaning and removal of the charred oily encrusted coating has been essential in order to minimize coffee bean contamination and fire hazards. In addition, high temperature roasting produced harmful insolubles such as the carcinogens noted in the 1974 U.S. Pat. No. 3,809,775 to Ganiaris.
Further details and drawbacks of widely used commercial roasting methods and machines may be found in Volume 1, pages 203 to 226, 235 to 238, of my two volume work entitled Coffee Processing Technology, published by the AVI Publishing Co. Inc., Westport, Conn., in 1963.
There have been a number of prior art efforts directed to a process of fluidization of coffee bean mass to achieve an improved roast. One such effort may be found in the 1958 U.S. Pat. No. 2,859,116 to Heimbs et al. This reference teaches the roasting of a coffee bean type material by a fresh upward hot air suspension of the beans in vertically conical roasting chamber. However, the patent does not disclose how to control the bean fluidization and the chamber temperature to produce a uniform bean roast without burning. The undesirable roasting vapor organic byproducts generated by the Heimbs method had to be purified before recirculation of the heating gas, a limitation overcome with the present invention.
In a 1962 U.S. Pat. No. 3,060,590 to Brown, a complicated continuous flow apparatus achieving fluidization of a thin sheet of solid particles by a plurality of downwardly directed air blast tubes is shown. The apparatus therein is vastly different from the present invention, and it is not particularly directed to roasting coffee beans. The process disclosed therein is incapable of creating a dense cubic floating bed of coffee beans in recirculating fluidized mass. Also, heat is lost by conduction from the bottom metal conveyor. An even more complicated downdraft apparatus is shown in Brown's 1966 U.S. Pat. No. 3,263,339 wherein baffles and deflectors are employed in an effort to thicken the fluidized particulate mass being processed. The complications and disadvantages of the Brown devices are made unnecessary by the present invention.
Another prior art reference disclosing a species of fluidization is the 1954 U.S. Pat. No. 2,876,557 to Ducatteau. That continuous processing apparatus reference discloses only in general terms a complex series of baffled compartments in which various upward air currents lift particles from one processing location to another, but gives no details to cover the processing of coffee beans therein. It is doubtful from the information actually supplied that successful coffee bean roasting could be accomplished by such an apparatus. The present invention is vastly different in both method and apparatus from that shown in the Ducatteau reference.
A 1964 U.S. Pat. No. 3,149,976 to J. L. Smith, Jr., assigned to Blaw-Knox Co. of Pittsburgh, Pa., shows a columnar roasting apparatus wherein fluidized particles cascade downwardly from plate to plate while warm air passes upwardly through the particles. That process and apparatus bears no resemblance to the present invention.
A 1969 U.S. Pat. No. 3,486,240 to Nowak et al, also assigned to Blaw-Knox, discloses a complicated multi-level and radially extending multi-chamber carousel type roasting device employing a heated gaseous fluid updraft to fluidize particles. Baffle members and carefully aligned gas nozzles are utilized in the device to create an involved mushroom spraying effect within the particulate material being treated. The complications of apparatus and method disclosed therein are avoided in the present invention.
In another patent assigned to the Blaw-Knox Company, the 1968 U.S. Pat. No. 3,370,522 to Anderson et al, a high speed fluidization of roasting coffee beans is achieved in a complicated pressurized environment involving humidified heated gas and a pressure release. Such complicated processing apparatus and complicated processing requirements are shown to be unnecessary by the present invention.
Finally, several patents issued to H. L. Smith, Jr., U.S. Pat. Nos. 3,189,460, (1965); 3,328,894 (1967); 3,329,506 (1967); 3,345,181 (1967); 3,385,199 (1968); 3,447,338 (1969); 3,615,668 (1971 ) and 3,724,090 (1973) disclose pressurized roasting methods that employ a form of bean fluidization. The pressurized inert gas processes disclosed in those patents are of primary usefulness only in the roasting of the lower grades of Robusta coffee beans, wherein it is desirable to increase the acidity of the coffee bean to improve taste acceptance. The Smith apparatus is complicated by the requirement of inert gas pressurization, recycle condensate purge processes and rotating turret roast chambers which disadvantages, as well as others, are overcome by the present invention.
In view of the foregoing, a general object of the present invention is to provide an improved and simplified apparatus for batch or continuous roasting coffee beans that achieves a uniformity of bean roast not achieved by prior art methods.
Another object of the present invention is to transfer heat from air into each coffee bean within a fluidized bed at a uniform and controlled rate, so that heating of each bean is uniform and equilibrated, and so that there is no excessive temperature exposure, scorching or burning of any bean or portion thereof.
A closely related object of the present invention is to roast air mobilized coffee beans at a controlled low temperature which produces pyrolysis within the beans as evidenced by a darker bean cell interior than surface, and yet the roasting temperature does not liberate essential volatiles and oils from the beans thereby retaining the taste producing elements.
A further related object is to roast beans in a way and at a temperature that does not produce contaminating or polluting organic byproducts thereby enabling the roasting apparatus to remain clean and uncontaminated throughout repeated roasting cycles and further enabling the discharge of expended roasting gas into the atmosphere without introduction of undesirable air pollutants.
Still further objects of the present invention are to provide a batch or continuous coffee roasting apparatus that overcomes the limitation of prior art fluidized bed coffee roasters, that has a size which may be varied from industrial capacity to home use, and that is uncomplicated in design, inexpensive to manufacture, simple and inexpensive to operate, and that requires very little cleaning or maintenance.